The invention relates to a protective arrangement with a rolling bearing unit with ABS capability that has a structurally integrated angle transmitter that is connected to a rotatable bearing race or rolling-element race so that it can rotate and has permanent magnet poles for coupling with an external sensor. Said protective arrangement is in the form of a protective cap or protective hood.
The use of a xe2x80x9cpulse seal, on non-driven passenger-car wheels for the purpose of implementing ABS is known (cf Heinrich Hofinann and Oswald Bayer xe2x80x9cABS-fxc3xa4hige Radlagerxe2x80x9d[Wheel Bearings with ABS Capability], preprint from xe2x80x9cWxc3xa4ilzlagertechnikxe2x80x94Industrietechnikxe2x80x9d [Rolling Bearing Systemsxe2x80x94Industrial Engineering] 1990 by FAG Kugelfischer, Schweinfurt). Here, the seal rotates with the wheel, a sheet- metal insert in the seal being provided with apertures, thereby allowing pulses to be derived electromagnetically in accordance with the angular position and speed of rotation. This angular pulse generator or encoder integrated into the rolling bearing unit is a significant functional component of the anti-lock brake system (ABS) of the vehicle and is therefore relevant to safety. Current ABS angle transmitters integrated into the wheel bearing are constructed from [[strong]] hard magnetic material to form a multiplicity of permanent magnet poles. When storing and transporting corresponding rolling bearing units with ABS capability, care should therefore be taken to ensure that the angle transmitter is not exposed to interfering external magnetic fields, which give rise to faults in magnetic angle encoding and can thus cause accidents when driving. Contamination of the environment within which the angle transmitter is installed by foreign bodies should moreover be prevented.
The object on which the invention is based is thus to increase the reliability and safety of rolling bearing units with ABS capability from the technical point of view when storing and transporting them. This should be accomplished with a minimum of outlay on construction, additional weight and space, ease of handling and assembly being desired at the same time.
To achieve this object in the case of a protective arrangement with the features stated at the outset, the invention proposes to arrange a [[weak]] soft magnetic cover on the rolling bearing unit at a distance from the angle transmitter in such a: way that a magnetic shield is formed between the angle transmitter and the environment outside. The [[weak]] soft magnetic material of the cover according to the invention prevents intruding external magnetic fields and thus protects the angle transmitter installed in the rolling bearing unit from external magnetic fields in a simple, effective and economical manner. Protection is furthermore also provided against ferrite contamination and other types of contamination. When the time comes to install the rolling bearing unit in the motor vehicle, the protective cover according to the invention can be handled easily and removed quickly. It can be configured not only as a disposable item but can also easily be configured to be reusable, allowing a single protective cover to be used for the storage and transportation of a large number of rolling bearings with ABS capability. Overall, this increases the economic viability of the ABS rolling-bearing protection system according to the invention.
In many cases, bearing races are formed from steel or some other ferromagnetic material. In this regard, a development of the invention proposes that the [[weak]] soft magnetic cover should be arranged in direct contact with one or both of the opposite bearing races. The interfering external magnetic fields can be diverted past the angle transmitter with greater reliability. Another advantage of this development is that one or both bearing races serve as a bearing surface for the shielding cover, ensuring defined positioning of the shielding cover on the rolling bearing unit.
It is within the scope of the invention that there should be a clearance or space, filled with air or some other nonmagnetizable substance, between the [[weak]] soft magnetic cover and the angle transmitter to ensure that effective magnetic shielding without disruption by external magnetic fields is achieved. This is taken into account by an advantageous development of the invention, according to which the shielding cover is arranged with an air gap relative to the angle transmitter and its installation space. It is particularly expedient if this air gap is formed between the annular space bounded by the two bearing races and the shielding cover.
Handling and transportation are easier if, in accordance with another development, the [[weak]] soft magnetic cover is secured on the rolling bearing unit by means of a flexible wrapping, e.g. a plastic film. This can be wound completely or partially around the rolling bearing unit and the shielding cover and can thus be useful in addition for keeping out dirt particles.
To enable the shielding cover to be mounted on the rolling bearing unit and released from it quickly, the shape of a hood or cap is expedient for the cover, an approximately hollow-cylindrical inner wall having a diameter that is greater than an external extent of the rolling bearing, in particular of an outer circumference or outer race. The shielding cover or protective cap or hood can thus be mounted on and removed from the rolling bearing unit easily. The protective cap or hood can be fixed in its position by means of the above-mentioned plastic film or packaging inserts in a packing carton.
The general inventive idea includes within its scope a specific configuration of the protective cap or hood for the protective arrangement explained above with a rolling bearing unit with ABS capability. For the purpose of achieving the object mentioned at the outset, the protective cap or hood is distinguished by the fact that it is produced from [[weak]] soft magnetic, as far as possible highly permeable, material and has a rotationally symmetrical end wall, the outline or diameter of which is dimensioned to cover and shield one side or end of the rolling bearing unit. In axial section, the protective cap or hood is, according to the invention, divided into a central part and a rim component, which surrounds said central part in the manner of a ring and is offset parallel to the axis. The central part is intended to be congruent with the inner race of the rolling bearing, while the rim component serves to cover the outer race and an annular space between the inner and the outer race of the bearing. The angle transmitter to be shielded is expediently installed in the annular space. In rolling bearing units, the central part of the end wall is particularly suited to being placed in contact with the inner bearing race for the purpose of positioning the protective cap or hood, while the ring- type rim component then has a clearance with respect to the annular installation space of the angle transmitter owing to its cranked offset parallel to the axis. The resulting air gap between the annular installation space of the angle transmitter in the rolling bearing and the inside of the protective cap or hood effectively promotes shielding against external magnetic fields.
The hollow-cylindrical circumferential wall into which the end wall of the protective cap or hood merges is advantageously dimensioned with an inside diameter that leads to the formation of a clearance relative to the outer circumference of the rolling bearing unit. This allows the protective cap or hood to be mounted on or removed from the rolling bearing unit extremely quickly. It is important that the protective cap or hood is produced from highly permeable material, e.g. [[weak]] soft magnetic sheet iron with as low a carbon content as possible, at least in the zone or section that is intended to be congruent with the location of installation of the angle transmitter. In contrast, the central zone, which is not intended to lie opposite the angle transmitter, can have through cutouts or apertures and/or be formed by plastic.